The overall goal is to evaluate a program of primary prevention in young children at high risk for developing conduct problems and later antisocial behavior. This investigation is prompted by 1) the serious nature of childhood conduct problems; 2) their poor long- term prognosis; 3) their resistance to treatment; 4) the absence of preventive interventions studies for very young high-risk children; and 5) the paucity of intervention programs tailored to inner-city families. The timing for prevention experiments is ideal, since their design can now rest on rational bases derived from our current knowledge about risk factors for conduct problems and antisocial behavior. A randomized controlled clinical trial of a multisystemic, intensive intervention for families of high-risk preschoolers is proposed. Ninety-six inner-city preschoolers who have older siblings with court-documented histories of antisocial behavior will be randomly assigned to a year-long family-based intervention or to a no contact control group. The intervention will consist o clinic and home-based parenting skills training. Immediate and long-term (1 year) outcome of children receiving intervention and controls will be compared. Outcome variables, including parenting practices, child conduct problems and child social competence, will be assessed with blind observations in multiple settings, as well as by parent and teacher ratings, and structured diagnostic interviews. This study is unique in that 1) the preventive intervention is truly primary-it targets preschoolers who are at high risk for developing conduct problems and later antisocial behaviors but who do not yet display these behaviors; 2) it assesses the efficacy of an intensive, family- based preventive intervention for reducing a key risk factor for conduct problems-inadequate parenting practices; 3) the intervention is tailored to inner-city families; 4) recruitment, assessment and intervention procedures have been tested for feasibility; and 5) the prevention program has been manualized.